1. Field of the Invention
The invention relates to methods and apparatuses to monitor paging message, and more particularly to methods and apparatuses to monitor paging message during cell selection/reselection without paging lost.
2. Description of the Related Art
Due to mobile communication technology advancements in recent years, various communications services, such as voice call services, data transfer services, and video call services, etc., may be provided to users regardless of their locations. Most mobile communications systems are multiple access systems in which access and wireless network resources are allocated to multiple users. The multiple access technologies employed by the mobile communications systems include the 1x Code Division Multiple Access 2000 (1x CDMA 2000) technology, the 1x Evolution-Data Optimized (1x EVDO) technology, the Orthogonal Frequency Division Multiplexing (OFDM) technology, and the Long Term Evolution (LTE) technology. Evolved from the LTE technology, the LTE Advanced technology is a major enhancement of the LTE standard. The LTE Advanced technology should be compatible with LTE equipment, and should share frequency bands with the LTE communications system. One of the important LTE Advanced technology benefits is its ability to take advantage of advanced topology networks, wherein optimized heterogeneous networks have a mix of macros with low power nodes such as picocells, femtocells and new relay nodes.
Generally, a User Equipment (UE) in the mobile communications system monitors a paging channel in both a Radio Resource Control (RRC)_connected state and an RRC idle state. The UE is in the RRC_connected state when an RRC connection has been established. If no RRC connection is established, the UE is in the RRC_idle state. In the RRC_idle mode, the UE monitors a paging channel to detect possible incoming calls (or called mobile terminated call, MT call), system information change, Earthquake and Tsunami Warning System (ETWS) notifications (for ETWS capable UEs) and Commercial Mobile Alert System (CMAS) notifications (for CMAS capable UEs). In the RRC_connected mode, the UE monitors a paging channel and/or system information block type 1 contents to detect system information changes, ETWS notifications (for ETWS capable UEs) and CMAS notifications (for CMAS capable UEs).
Conventionally, during a cell selection or reselection procedure, the UE does not listen to or monitor the paging channel before all of the paging parameters required for deriving the occurrence time of the paging frames (PF) and paging occasions (PO) have been received from the network. Those paging parameters required for deriving the structure (i.e. the occurrence time) of the paging frames and paging occasions are respectively carried in the master information block (MIB) and the system information block type 2 (SIB2). The paging occasion (PO) defines the time for the communication apparatus to wake up (when required) and receive the paging indication messages, and the paging frame (PF) is a radio frame which may contain one or multiple paging occasions. FIG. 1 shows a cell selection procedure. There is an interruption interval after the beginning of the cell selection (that is, a suitable cell has been determined and a synchronization procedure between the UE and the suitable cell has begun) up to the time when the SIB2 has been received. During the interruption interval, the paging message and ETWS/CMAS notifications are unable to be received due to no paging parameters. Therefore, if any paging occasion occurs in the interruption interval, such as the paging occasion 101 shown in FIG. 1, the UE would miss the paging occasion and be unable to receive the paging messages transmitted at that paging occasion.
FIG. 2 shows a cell reselection procedure. In the cell reselection procedure, there is also an interruption interval, during which the paging message and ETWS/CMAS notifications are unable to be received from the target cell due to no paging parameters, after beginning of the cell reselection (that is, a target cell has been determined and a synchronization procedure between the UE and the target cell has begun) and until the SIB2 has been received from the target cell. If any paging occasion occurs in the interruption interval, such as the paging occasion 201 shown in FIG. 2, the UE would miss the paging occasion and be unable to receive the paging messages transmitted at that paging occasion. In addition, if the UE still wants to receive paging messages from the original serving cell, the UE may switch back to the monitoring of the paging channel corresponding to the original serving cell at the corresponding paging occasion, such as the paging occasion 202 shown in FIG. 2. However, one disadvantage of switching back to the monitoring of the original paging channel is that the paging message may be lost because the cell reselection is generally triggered when the signal quality of the original serving cell has deteriorated. Another disadvantage is that the interruption interval may be prolonged, due to the situation where the system information block type 1 (SIB1) 203 of the target cell colliding with the paging occasion 202 is missed.
Therefore, methods and apparatuses to monitor paging message during cell selection/reselection without paging lost are highly required.